You don't need a pass to make reservations most of the time. Have a look at : https://www.seat61.com/interrail-and-eurail-reservations.htm

It is always better to book through the company : less/no fees, sometimes seat map, etc.

Feel free to ask further questions, mentioning route and travel date. We'll gladly help !

Of course, the mobile pass works as good as the paper one.

You don't need your pass to make seat reservations, make seat reservations via the operator's own websites to save a bit of money.

Check the guide here:

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

Thank you so much for your answer. I'm about to buy the mobile pass. Just wanted to make sure; you can make all the reservations with a mobile pass online. You dont need a paper pass to make a reservation? 

You can make all reservations online yes. You don't need a pass to make them, you should simply be able to show the pass onboard.

If it wasn't possible, people wouldn't choose the paper pass -> don't worry!

Have a look at the link I posted. For example in Germany you follow the same process whether you have a pass or a regular ticket (which doesn't include a reservation).

If you would really like a paper pass, you can buy one at the international ticket office at Schiphol Airport or Amsterdam Centraal.